This dissertation explains how international disputes over the legal foundations of United States imperial expansion became sites of unanticipated struggle over the legitimacy of the American justice system. Between the mid nineteenth century and the early twentieth, the United States submitted to a series of international tribunals designed to award monetary compensation for loss of life and property resulting from the wave of territorial acquisitions that transformed the nation into a global empire. These claims commissions depoliticized the dispossession that resulted from annexation by characterizing it as a form of exchange that could be retroactively settled through arbitration. The model of justifying expansion through claims settlement came into crisis when foreign nationals from Panama, the West Indies, and Mexico who were living in United States territories turned to these tribunals to argue that the US government authorized forms of state violence and labor coercion in violation of the international norms known as the “standard of civilization.” By demonstrating how claimants used seemingly technical calculations of market value compensation to question the government’s ability to protect life and property within its borders, the dissertation uncovers a forgotten moment of struggle over the limits and possibilities of international law to address structural injustices within the American legal system.